Number management system, number management method, number management device and number management program

ABSTRACT

A number management unit (11) of a number management system (1) generates a transaction using number portability information including a telephone number and encrypted connection destination information, newly generates a block using multiple transactions, approves the generated block, and stores the block in a number database (13) as a blockchain. A number resolution unit (12) searches transactions in the blockchain using a telephone number that is a query target as a key, extracts and decrypts the encrypted connection destination information corresponding to the query telephone number, and sends the connection destination information corresponding to the query telephone number as a response.

TECHNICAL FIELD

The present invention relates to a number management system, a numbermanagement method, a number management apparatus, and a numbermanagement program, in which blockchain technology is utilized in orderto realize number portability in a telephone line network.

BACKGROUND ART

Conventionally, in an IP (Internet Protocol) network, an ENUM (E.16 4Number Mapping) system has been proposed as a mechanism by which anapparatus in a communication provider network (an SIP (SessionInitiation Protocol) server, etc.) performs association of a telephonenumber and a URI (Uniform Resource Identifier). In the ENUM system, anSIP server that is installed in a network of a communication providerperforms routing based on information of a connection destination byquerying information of a connection destination (IP address, domainname, etc.) for a telephone number of a terminal (IP telephone, etc.)serving as a connection destination to the ENUM server (see NPL 1).

Also, a number portability scheme by which a fixed telephone number canbe carried around freely between communication providers in an IPnetwork accompanying a transition from a PSTN (Public Switched TelephoneNetwork) to an IP network has been considered (see NPL 2).

In the number portability scheme according to NPL 2, a number database(number DB) for performing centralized management of number portabilityinformation of communication providers is included in theabove-described ENUM server (ENUM authority server), and due to the SIPserver of each communication provider accessing the ENUM server of thecommunication provider to which the SIP server belongs, the SIP serverresolves whether or not the telephone numbers have been transferred(ported out) to another network, and performs communication by acquiringinformation of the connection destination (connection destinationinformation).

Specifically, as shown in FIG. 10, in an ENUM system 1000, in the casewhere a telephone number (incoming number) attached to a request from anSIP server is a query for a telephone number managed in the localnetwork, the ENUM server sends the connection destination information asa response from the number DB of the ENUM server (see reference sign αin FIG. 10). On the other hand, if the telephone number attached to therequest is a telephone number managed by an ENUM server of anothernetwork, a request is performed to the ENUM server of the other networkmanaging the telephone number, and the obtained connection destinationinformation is sent as a response to the request source (see referencesign β in FIG. 11).

Thus, with the current Japanese telephone line network, an ENUM systemis employed in order to realize number portability, and as a specificmechanism therefor, in a routing scheme, a “transmitting-side DBreference scheme”, that is, a scheme in which the provider of the callsource realizes connection of the call even if the DB (number database)of another provider is referenced is employed. Also, in the databasescheme, an “on-premises separate DB scheme”, that is, a scheme in whicheach company possesses its own number DB, is employed.

CITATION LIST Non Patent Literature

-   [NPL 1] “Common interconnection interface for carrier ENUM”, TTC    JJ-90.31, [online], Telecommunication Technology Committee, Aug. 29,    2018, [searched for on Jun. 13, 2019], Internet <URL:    https://www.ttc.or.jp/application/files/4715/5418/5873/JJ-90.31v4.pdf>-   [NPL 2] “Handling number portability”, [online], Ministry of    Internal Affairs and Communications, Jul. 28, 2016, [searched for on    Jun. 13, 2019], Internet <URL: http://www.soumu.go.jp/main    content/000433169.pdf>

SUMMARY OF THE INVENTION Technical Problem

As described above, in a conventional ENUM system, the“transmitting-side DB reference scheme” is employed as the routingscheme, and the “on-premises separate DB scheme” is employed as thedatabase scheme. However, in the number portability scheme in which thisENUM system is employed, there is a problem in that when an ENUM serverof a certain communication provider breaks down, it is no longerpossible to resolve numbers for the number range managed by thatcommunication provider.

Also, in the current state, only large-scale communication providers(large-scale providers) have ENUM servers, and small-scale communicationproviders (small-scale providers) have the ENUMs of large-scaleproviders manage connection destination information corresponding totelephone numbers (hereinafter referred to as “number information”), andthus the following problems are also present.

(1) High reliability is required in order to construct an ENUM system.For this reason, a large cost is required, and the burden is large for asmall-scale provider.

(2) When a small-scale provider wants to perform updating of data, thesmall-scale provider needs to make a request to a large-scale providerto perform a change. For this reason, there is no guarantee thatupdating can be performed in real time.

(3) When a communication provider withdraws, there is a risk that itwill no longer be possible to resolve the portability destinations ofthe numbers being managed by that communication provider.

There is also a problem in that if all providers are allowed to possessthe database through some method in order to solve the above-describedproblems, the communication providers can easily acquire whichcommunication providers the telephone number contractors are contractedwith by merely referencing their own databases, and the risk ofinformation leakage resulting from loss or theft or the like of storagedevices possessed by the communication providers increases.

The present invention was made in view of such background circumstances,and the present invention aims to improve availability andconfidentiality of number portability information that is to be used inan ENUM system.

Means for Solving the Problem

A number management system according to the present invention is anumber management system including a plurality of number managementapparatuses for managing number portability information including atelephone number and connection destination information for thetelephone number, in which the plurality of number managementapparatuses each include a number management unit configured to managethe number portability information as a blockchain, and a numberresolution unit configured to send the connection destinationinformation corresponding to a query telephone number as a response, thenumber management unit includes a request reception unit configured toreceive a number update request including the number portabilityinformation, a transaction generation unit configured to generate atransaction including encrypted connection destination informationobtained by encrypting the connection destination information includedin the number portability information using a predetermined encryptionkey, and the telephone number, a block suggestion unit configured toacquire the transactions generated according to a plurality of saidnumber update requests, generate a newly-suggested block including atransaction group obtained by aggregating the acquired plurality oftransactions, and transmit the generated suggested block to therespective plurality of number management apparatuses creating theblockchain, and a block approval unit configured to receive thesuggested block, approve the suggested block by confirming apredetermined normality of the suggested block, and store the suggestedblock by connecting the suggested block to a block stored as theblockchain in a storage unit, and the number resolution unit includes aquery reception unit configured to receive a query request including thequery telephone number, a data management unit configured to searchtransactions in the blockchain using the query telephone number as a keyand extract the encrypted connection destination informationcorresponding to the query telephone number, and a decryption processingunit configured to decrypt the encrypted connection destinationinformation using a decryption key and send the connection destinationinformation corresponding to the query telephone number as a response.

Effects of the Invention

According to the present invention, it is possible to improveavailability and confidentiality of number portability information to beused in an ENUM system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an overall configuration of a numbermanagement system according to the present embodiment.

FIG. 2 is a block diagram showing an example of a hardware configurationof a computer that realizes functions of a number management apparatusaccording to the present embodiment.

FIG. 3 is a block diagram showing a functional configuration of a numbermanagement apparatus according to the present embodiment.

FIG. 4 is a diagram showing blocks stored as a blockchain in a numberdatabase of a number management apparatus.

FIG. 5 is a diagram showing blocks stored as a blockchain in a numberdatabase of a number management apparatus.

FIG. 6 is a sequence diagram showing a flow of processing performed by anumber management unit according to the present embodiment.

FIG. 7 is a sequence diagram showing a flow of processing performed by anumber resolution unit according to the present embodiment.

FIG. 8 is a diagram showing an overall configuration of an ENUM systemincluding a number management system according to Variation 1 of thepresent embodiment.

FIG. 9 is a sequence diagram showing a flow of processing performed bythe ENUM system including the number management system according toVariation 1 of the present embodiment.

FIG. 10 is a diagram showing an overview of number management processing(number in own network) in a conventional ENUM system.

FIG. 11 is a diagram showing an overview of number resolution processing(query to another network) in a conventional ENUM system.

DESCRIPTION OF EMBODIMENTS

Next, a number management system 1 and the like according to a mode forimplementing the present invention (hereinafter referred to as “presentembodiment”) will be described.

FIG. 1 is a diagram showing an overall configuration of the numbermanagement system 1 according to the present embodiment.

As shown in FIG. 1, the number management system 1 is constituted due tonumber management apparatuses 10 serving as blockchain creationapparatuses of communication providers (written as “providers” in thedrawings) being communicably connected to each other. In FIG. 1, as anexample, a number management apparatus (blockchain creation apparatus)10A of a communication provider A, a number management apparatus(blockchain creation apparatus) 10B of a communication provider B, and anumber management apparatus (blockchain creation apparatus) 10C of acommunication provider C are shown. The number of number managementapparatuses 10 is not limited to this, and it is sufficient thatmultiple number management apparatuses (blockchain creation apparatuses)10 are communicably connected to each other.

The information that is managed in this number management system 1 isinformation for number portability (hereinafter referred to as “numberportability information”). Number portability is a mechanism by whicheven if a communication provider being used by a user is changed, theuser can use the service of the changed communication provider withoutchanging his or her telephone number. Each communication providerperforms number resolution by holding number portability information asinformation obtained by updating the connection destination informationfor the number information of that provider (the telephone numbers andthe connection destination information corresponding to the telephonenumbers) to connection destination information addressed to anotherprovider.

In the present embodiment, the number management apparatus 10 of eachcommunication provider stores the number portability information of allcommunication providers that participate in the blockchain in a numberdatabase (DB) 13 as a blockchain. Also, the number management apparatus10 includes a function (number resolution function) of responding to aquery (request) for connection destination information from an SIPserver or the like. That is, the number management apparatus 10 includesa number management unit 11 and a number resolution unit 12. The numbermanagement unit 11 manages number portability information including atelephone number and connection destination information for thetelephone number as a blockchain. The number resolution unit 12 providesconnection destination information corresponding to a query telephonenumber in response to a query for a connection destination correspondingto a given query telephone number. The number management unit 11 and thenumber resolution unit 12 in the same number management apparatus 10 areunder the management of the same provider and have a correspondencerelationship.

Note that in the present embodiment, the number management apparatuses10 that participate in the blockchain are premised not on apublicly-open type of blockchain in which anyone can participate, whichis used in financial transactions, but on a Permissioned type ofblockchain using a service in which the blockchain is used among limitedmembers. For example, the members participating in the blockchain arecommunication providers to which telephone numbers have been dispensedfrom the Ministry of Internal Affairs. However, there is no limitationto such specific communication providers, and specific individuals suchas those shown in later-described Variation 3 may also be included.

<Number Management Apparatus>

Next, the number management apparatus 10 according to the presentembodiment will be described.

The number management apparatus 10 is a blockchain creation apparatusthat manages number portability information of members (communicationproviders) that participate in the blockchain. This number managementapparatus 10 is connected to a number management apparatus 10 of anothercommunication provider that participates in the blockchain and isconnected to a system of a communication provider (e.g., a providerterminal). Note that the number management apparatuses 10 (10A, 10B,10C) include the same functions, which will be described hereinafter.

FIG. 2 is a hardware configuration diagram showing an example of acomputer 900 that realizes the functions of the number managementapparatus 10 according to the present embodiment. The computer 900includes a CPU (Central Processing Unit) 901, a ROM (Read Only Memory)902, a RAM (Random Access Memory) 903, an HDD (Hard Disk Drive) 904, aninput/output I/F (Interface) 905, a communication I/F 906, and a mediaI/F 907.

The CPU 901 operates based on the program stored in the ROM 902 or theHDD 904 and performs control using the units shown in FIG. 1 (numbermanagement unit 11, number resolution unit 12). The ROM 902 stores aboot program to be executed by the CPU 901 during startup of thecomputer 900, a program according to the hardware of the computer 900,and the like.

The CPU 901 controls an input apparatus 910 such as a mouse or akeyboard, and an output apparatus 911 such as a display or a printer,via the input/output I/F 905. The CPU 901 acquires data from the inputapparatus 910 and outputs the generated data to the output apparatus911, via the input/output I/F 905.

The HDD 904 (storage apparatus) stores programs to be executed by theCPU 901 and data (number database 13, etc.) to be used by the programs.The communication I/F 906 receives data from another apparatus (notshown) (e.g., another number management apparatus 10, an SIP server 30,etc.) via a communication network (e.g., a network (NW) 5) and outputsthe received data to the CPU 901, and transmits the data generated bythe CPU 901 to another apparatus via a communication network.

The media I/F 907 reads a program or data stored in a recording medium912 and outputs it to the CPU 901 via the RAM 903. The CPU 901 loads aprogram for target processing from the recording medium 912 on the RAM903 via the media I/F 907 and executes the loaded program. The recordingmedium 912 is an optical recording medium such as a DVD (DigitalVersatile Disc) or a PD (Phase change rewritable Disk), amagneto-optical recording medium such as an MO (Magneto Optical disk), amagnetic recording medium, a conductor memory tape medium, asemiconductor memory, or the like.

For example, if the computer 900 functions as the number managementapparatus 10 according to an embodiment, the CPU 901 of the computer 900realizes the functions of the number management unit 11 and the numberresolution unit 12 of the number management apparatus 10 by executingthe program loaded on the RAM 903. Also, the data in the RAM 903 isstored in the HDD 904. The CPU 901 reads a program for target processingfrom the recording medium 912 and executes the program. In addition, theCPU 901 may also load the program for the target processing from anotherapparatus via a communication network (network 5).

<Number Management Unit>

FIG. 3 is a block diagram showing a functional configuration of thenumber management apparatus 10. As shown in FIG. 3, the numbermanagement apparatus 10 is constituted by including the numbermanagement unit 11, the number resolution unit 12, and the numberdatabase 13.

Furthermore, the number management unit 11 is constituted by including arequest reception unit 111, a transaction generation unit 112, a blocksuggestion unit 113, and a block approval unit 114.

The request reception unit 111 receives a number update request from acommunication provider (provider terminal) or the like via theinput/output unit. The telephone number (e.g.: 0312345678) that is to besubjected to number portability, and connection destination informationof the other communication provider that is the number changedestination (hereinafter referred to also as “accepting providerinformation” in some cases) (e.g.: 0312345678@abc.ne.jp) are included inthe number update request. The number portability information isconstituted by including the telephone number and the accepting providerinformation, which is the connection destination information of thechange destination.

Upon receiving a number update request, the request reception unit 111generates a number update suggestion that includes the telephone numberand the accepting provider information and outputs the number updatesuggestion to the transaction generation unit 112.

Upon receiving the transaction generated by the transaction generationunit 112, the request reception unit 111 transmits a number updateinstruction including the received transaction to the block suggestionunit 113 of the number management apparatus 10 determined based on thepredetermined logic (block suggestion unit selection logic) among thenumber management apparatuses 10 creating the blockchain. Thetransaction is generated using the number portability information asinformation that is managed and stored in the blockchain. For example,the predetermined logic may set any number management apparatus 10 (anumber management apparatus 10 that has a high processing performance,is adjacent distance-wise, etc.) in advance, and may randomly determinethe number management apparatus 10. The block suggestion unit 113 of thenumber management apparatus 10 may also be included in the candidatesfor determination.

Upon receiving the number update suggestion, the transaction generationunit 112 confirms the normality of the information (number portabilityinformation) of the telephone number and the accepting providerinformation, which is the connection destination information of thechange destination, the information being the suggestion content of thenumber update suggestion.

The confirmation of the normality performed by the transactiongeneration unit 112 is, for example, performing authentication ofwhether or not the telephone number is in a stipulated format (number ofdigits, etc.), or whether or not the accepting provider information isin a stipulated format.

If the normality is confirmed, the transaction generation unit 112generates a transaction that is managed and stored in a blockchain forthe number portability information. Then, the transaction generationunit 112 outputs a number update suggestion response including thegenerated transaction to the request reception unit 111.

Here, the transaction generation unit 112 encrypts the connectiondestination information in the number portability information using apredetermined encryption key and generates a transaction. That is, thetransaction generation unit 112 generates a transaction includingencrypted connection destination information obtained by encrypting theconnection destination information included in the number portabilityinformation using a predetermined encryption key, and a telephonenumber. Due to the connection destination information being encrypted inthis manner, it is no longer possible to find out the correspondencebetween the telephone number and the connection destination informationby looking at the transaction.

It is preferable that the encryption keys used by the transactiongeneration units 112 of the number management apparatuses 10 aredifferent from each other. This is because when the same encryption keyis used by all of the number management apparatuses 10, if thedecryption key corresponding thereto is specified, all of thetransactions (encrypted connection destination information) can bedecrypted.

Also, it is preferable that a decryption key corresponding to anencryption key used by the transaction generation unit 112 of eachnumber management apparatus 10 is allowed to be held by a numbermanagement apparatus 10 other than that number management apparatus 10.That is, it is preferable that the decryption key corresponding to theencryption key used by a predetermined number management unit(transaction generation unit 112) is held by one of the numberresolution units 12 other than the number resolution unit 12corresponding to the predetermined number management unit 11 (in thesame apparatus). This is for avoiding a case in which the communicationprovider holding the number management apparatuses 10 intentionallydecrypts the encrypted connection destination information. Inparticular, it is preferable that the decryption key corresponding tothe encryption key allowed to be held by multiple number managementapparatuses 10 (number resolution units 12) other than the numbermanagement apparatus 10. This is because if the decryption keycorresponding to the encryption key is given to only one numbermanagement apparatus 10, later-described number resolution processingcan no longer be performed if breakdown occurs in the number managementapparatus 10 or the like.

For example, as shown in FIG. 4, the transaction generation unit 112includes identification information (decryptable provider informationshown in FIG. 4) of the number management apparatus 10 (numberresolution unit 12) holding the decryption key corresponding to theencryption key used in this instance of encryption in the transaction.This makes it possible to specify the query destination for when theencrypted connection destination information of the transaction is to bedecrypted.

Note that the transaction generation unit 112 may also not output thegenerated transaction to the request reception unit 111, and maydetermine the block suggestion unit 113 of one of the number managementapparatuses 10 creating the blockchain based on the predetermined logic(block suggestion unit selection logic), and transmit the number updateinstruction including the generated transaction to the determined blocksuggestion unit 113.

The block suggestion unit 113 aggregates the number update instructionsreceived from the number management apparatuses 10 creating theblockchain, and generates a block including multiple transactions(hereinafter referred to as a “transaction group”). This block includesthe aggregated transactions (transaction group) and a hash value (alater-described “previous block hash value”) calculated using thetransaction group of the most recent block at the current time among theblocks stored as the blockchain in the number database 13.

FIG. 4 is a diagram showing blocks stored as a blockchain in the numberdatabase 13 of each number management apparatus 10.

Each block stores information on a transaction group and information ona “previous block hash value”. In the example shown in FIG. 4, the mostrecent (last-connected) block a at the current time stores a hash value(prior block hash value), which is a value calculated using a hashfunction on the transaction group of the block a−1, which is the blockthat is connected immediately prior thereto, and information on the mostrecent transaction group at that time.

When a suggested block is to be generated, the block suggestion unit 113uses a hash function to calculate the hash value of the transactiongroup for the most recent block (block a). Then, the block suggestionunit 113 generates, as the suggested block (block a+1), a blockincluding the calculated hash value (previous block hash value) and thenewly-aggregated transaction group.

Upon generating the newly-suggested block (block a+1), the blocksuggestion unit 113 transmits a number update approval request includingthat block to the block approval units 114 of the number managementapparatuses 10 creating the blockchain.

Returning to FIG. 3, upon receiving the number update approval request,the block approval unit 114 confirms the normality of the block includedin the number update approval request. The confirmation of the normalityis performed as follows, for example. The block approval unit 114calculates a hash value using the transaction group in the most recentblock (block a) of the blockchain stored in the number database 13 ofthe number management apparatus 10. Then, the block approval unit 114determines whether or not the previous block hash value included in thenewly-suggested block a+1 in the number update approval request and thecalculated hash value match each other. Then, if the hash values matcheach other, the block approval unit 114 approves the block as a normalblock, connects the block as the next block (block a+1) in theblockchain to the block a, and stores the result (see FIG. 5).

The same transaction (number portability information) is stored in thenumber databases 13 of all of the number management apparatus 10 due tothe suggested block being approved (the normality being confirmed) bythe block approval units 114 of the number management apparatuses 10creating the blockchain.

<Number Resolution Unit>

Returning to FIG. 3, the number resolution unit 12 will be described. Inthe ENUM system, the number resolution unit 12 realizes a function (ENUMserver number resolution function) of responding to a query (request)regarding connection destination information from an SIP server or thelike.

As shown in FIG. 3, the number resolution unit 12 is constituted byincluding the query reception unit 121, the data management unit 122,and the decryption processing unit 123.

The query reception unit 121 receives a query requesting connectiondestination information (accepting provider information) of a giventelephone number from an SIP server or the like. This query includes atelephone number serving as the query target of the current instance(hereinafter referred to as “query telephone number”). Also, the queryreception unit 121 outputs the query telephone number to the datamanagement unit 122 and receives the encrypted connection destinationinformation and the decryptable provider information corresponding tothe query telephone number. In addition to that, the query receptionunit 121 transmits the encrypted connection destination information tothe decryption processing unit 123 of the number management apparatus 10identified by the decryptable service provider information and receivesthe decrypted connection destination information. Note that if thenumber management apparatus 10 is included in the decryptable providerinformation, the number management apparatus 10 may also requestdecryption of the encrypted connection destination information to thedecryption processing unit 123 of the number management apparatus 10.Also, the query reception unit 121 transmits the connection destinationinformation received from the decryption processing unit 123 to the SIPserver or the like that is the query source as a query response.

The data management unit 122 searches the transactions in the blockchainof the number database 13 using the query telephone number as a key,extracts the encrypted connection destination information correspondingto the query telephone number and outputs the encrypted connectiondestination information to the query reception unit 121. At this time,the data management unit 122 also transmits the decryptable serviceprovider information included in the transaction to the query receptionunit 121.

The decryption processing unit 123 decrypts the encrypted connectiondestination information received from the query reception unit 121 usingthe decryption key held by the decryption processing unit 123 andtransmits the result to the query reception unit 121. That is, thedecryption processing unit 123 decrypts the encrypted connectiondestination information using the decryption key and sends theconnection destination information corresponding to the query telephonenumber as a response.

<Processing Performed by Number Management Unit>

Next, a flow of processing performed by the number management unit 11according to the present embodiment will be described. FIG. 6 is asequence diagram showing a flow of processing performed by the numbermanagement unit 11 according to the present embodiment.

First, one of the number management apparatuses 10 included in thenumber management system 1 (e.g., the number management apparatus 10A)receives a number update request from a communication provider(communication provider terminal) or the like (step S1). The numberupdate request includes number portability information composed of thetarget telephone number (e.g., “0312345678”) and connection destinationinformation (accepting provider information) of another communicationprovider serving as the change destination for the telephone number(e.g., “0312345678@abc.ne.jp”). Note that the communication provider(communication provider terminal) may also transmit the number updaterequest to the number management apparatus 10 belonging to thecommunication provider, and may also transmit the number update requestto a number management apparatus 10 that creates the blockchain andbelongs to another communication provider. Thus, for example, the numberupdate request may also be transmitted from a provider terminal A of thecommunication provider A to a number management apparatus 10B of acommunication provider B.

Next, the request reception unit 111 of the number management apparatus10 that received the number update request extracts the numberportability information (the phone number and the accepting providerinformation serving as the change destination) included in the numberupdate request, and outputs a number update suggestion including thenumber portability information to the transaction generation unit 112 ofthe number management apparatus 10 (step S2).

Upon receiving the number update suggestion, the transaction generationunit 112 confirms the normality of whether or not the information on thetelephone number and the accepting provider information serving as thechange destination (number portability information), which is thesuggestion content of the number update suggestion, matches apredetermined regulation (format) (step S3).

If the normality of the number portability information is confirmed, thetransaction generation unit 112 encrypts the connection destinationinformation in the number portability information using the encryptionkey to generate the encrypted connection destination information, andgenerates a transaction including the telephone number, the encryptedconnection destination information, and the decryptable providerinformation (step S4). Then, the transaction generation unit 112 outputsthe number update suggestion response including the generatedtransaction to the request reception unit 111 (step S5). Note that, forexample, information stored in the storage unit (not shown) of thenumber management apparatus 10 in advance is used as the decryptableservice provider information.

Note that if the normality cannot be confirmed, the transactiongeneration unit 112 ends the processing. At this time, the transactiongeneration unit 112 may also send a response indicating that thenormality was not confirmed to the communication provider thattransmitted the number update request (communication provider terminal)via the request reception unit 111.

Next, the request reception unit 111 acquires the transaction includedin the number update suggestion response. The request reception unit 111transmits the number update instruction including the acquiredtransaction to the block suggestion unit 113 of the number managementapparatus 10 (e.g., the number management apparatus 10B) that wasdetermined based on the predetermined logic (block suggestion unitselection logic) among the number management apparatuses 10 creating theblockchain (step S6).

The block suggestion unit 113 of the number management apparatus 10 thatreceived the number update instruction aggregates the transactionincluded in the received number update instruction and the transactionsincluded in the other number update instructions received in additionthereto, and generates a block (suggested block) that includes multipletransactions (transaction group) (step S7). At this time, the blocksuggestion unit 113 calculates the hash value of the transaction groupfor the most recent block (block a in FIG. 4) and includes thecalculated hash value in the generated block as the “previous block hashvalue”.

Then, the block suggestion unit 113 transmits a number update approvalrequest including the generated block (suggested block) to the blockapproval units 114 of the number management apparatuses 10 (10A, 10C)creating the blockchain (step S8). Note that at this time, the blocksuggestion unit 113 outputs the number update approval request to theblock approval unit 114 of the number management apparatus 10B as well.

Upon receiving the number update approval request, the block approvalunits 114 of the number management apparatuses 10 approve the block byconfirming the normality of the block included in the number updateapproval request (step S9). Then, the block approval unit 114 stores theapproved block in the number database 13 connected to the block a as thenext block (block a+1 in FIG. 5) of the blockchain stored in the numbermanagement apparatus 10, and ends the processing.

Note that the block approval unit 114 performs the confirmation of thenormality by determining whether or not the values of the “previousblock hash value” included in the block and the hash value calculatedusing the transaction group of the most recent block (block a of FIG. 4)stored in the number database 13 of the number management apparatus 10match each other, and if they match, confirming that there is notampering and the like and the state is normal.

<Processing Performed by Number Resolution Unit>

Next, a flow of processing performed by the number resolution unit 12according to the present embodiment will be described. FIG. 7 is asequence diagram showing a flow of processing performed by the numberresolution unit 12 according to the present embodiment.

First, one (e.g., the number management apparatus 10A) of the numbermanagement apparatuses 10 included in the number management system 1receives a query for connection destination information from an SIPserver or the like (step S21). This query includes a telephone number(query telephone number) serving as a query target. Next, the queryreception unit 121 of the number management apparatus 10 that receivedthe query extracts the query telephone number included in the query andtransmits the query telephone number to the data management unit 122 asan accepting provider information acquisition request (step S22).

The data management unit 122 searches the transactions of the blocks inthe number database 13 (FIG. 3) using the query information as a key andextracts the transaction corresponding to the query telephone number(step S33). Then, the data management unit 122 outputs an acceptingprovider information response including the encrypted connectiondestination information and the decryptable provider information of theextracted transaction to the query reception unit 121 (step S24).

The query reception unit 121 transmits the decryption request includingthe encrypted connection destination information to the decryptionprocessing unit 123 of the number management apparatus 10 identified inthe decryptable provider information of the received accepting providerinformation response (step S25). Note that if the number managementapparatuses 10 identified in the decryptable provider informationinclude the number management apparatus 10, the decryption request mayalso be transmitted to the decryption processing unit 123 of the numbermanagement apparatus 10. Also, if multiple number management apparatuses10 are included in the decryptable service provider information, whenthe decryption response is not obtained within a predetermined amount oftime after the decryption request is transmitted to one numbermanagement apparatus 10, the query reception unit 121 may also transmitthe decryption request to another number management apparatus 10. Thequery reception unit 121 may also transmit the decryption request tomultiple number management apparatuses 10 at the same time and obtainthe decryption response.

Upon receiving the decryption request, the decryption processing unit123 decrypts the encrypted connection destination information using thedecryption key held by the decryption processing unit 123 to return itto connection destination information in plain text (data that has notbeen encrypted) (step S26), and transmits the plain text connectiondestination information to the query reception unit 121 as a decryptionresponse (step S27).

Then, the query reception unit 121 transmits a query response includingthe connection destination information corresponding to the querytelephone number to the SIP server and the like, which is the querysource (step S28).

In this manner, each number management apparatus (blockchain creationapparatus) 10 of the number management system 1 according to the presentembodiment can store not only the number portability informationrelating to the telephone numbers managed by the number managementapparatus 10, but also the number portability information of all members(communication providers) that participate in the blockchain.Accordingly, for example, even if the number management apparatus 10 ofa given communication provider breaks down, number resolution can becontinued due to the number portability information of all members(communication providers) that participate in the blockchain beingstored in the number management apparatuses 10 of the othercommunication providers. Accordingly, it is possible to improve theavailability of the number portability information that is used in theENUM system.

Also, by providing each number management apparatus 10 with the functionof an ENUM server, the number portability information of all membersthat participate in the blockchain is stored in the other numbermanagement apparatuses 10 even if one of the number managementapparatuses 10 breaks down, and therefore it is possible to eliminatethe need to increase the degree of reliability for the number managementapparatuses 10 including the functions of individual ENUM serverscompared to an ENUM server of a conventional ENUM system. Accordingly,the cost can be reduced. Also, during updating of the number portabilityinformation, a small-scale provider need only transmit the number updaterequest to one of the multiple number management apparatuses 10 creatingthe blockchain, and therefore it is possible to eliminate the need torequest that a specific large-scale provider performs the change.Accordingly, it is possible to remove a barrier of entry to a telephoneline network for a small-scale provider.

Also, due to a portion (connection destination information) of thenumber portability information being encrypted and stored in theblockchain as in the present embodiment, it is possible to increase theconfidentiality of the number portability information.

For example, if the number portability information is not encrypted, allof the number information (telephone numbers and accepting providerinformation for the telephone numbers) held by the providers will bedistributed in plain text to all of the providers connected by theblockchain. For this reason, a provider can easily acquire whichproviders the telephone number contractors are contracted with by merelyreferencing the data of their own blockchain (number database 13). Interms of the properties of a service called number portability,referencing of data in a blockchain in order to reference the providerinformation of a call destination during an outbound telephone call isallowed, but applications other than resolution of a telephone calldestination, such as use of the data for the purpose of recruiting auser who has been accepted by another provider do not match the originalintent of number portability and are problematic. As in the presentembodiment, it is possible to prevent providers from being able toeasily find out which providers telephone number contractors arecontracted with by encrypting a portion of the number portabilityinformation. Furthermore, due to an encryption key and a decryption keycorresponding thereto being dispersed to separate number managementapparatuses 10 as in the present embodiment, a query to another provideris generated, and therefore that action will be discovered, which servesas a deterrent, thus making it possible to more reliably preventunauthorized use of number portability by a provider.

Also, for example, in a case where the number portability information isnot encrypted, if the data in the blockchain (number database 13) leaksto a third party during exchange between providers of the blockinformation, or due to loss, theft, or the like of a storage devicepossessed by the providers, there is a risk that the number informationwill be misused. By encrypting a portion of the number portabilityinformation as in the present embodiment, even if the data in theblockchain is leaked, there is no longer a risk that the numberportability information will be leaked to a third party as long as thedecryption key for decrypting the connection destination information isnot leaked.

Also, by allowing multiple number management apparatuses 10 to hold thedecryption key corresponding to one encryption key as in the presentembodiment, it is possible to continue the number resolution processingin the overall system even if breakdown occurs in a specific numbermanagement apparatus 10, and thus it is possible to improve theavailability of the number portability information.

<<Variation 1>>

Next, Variation 1 of the number management system 1 according to thepresent embodiment will be described.

In the number management system 1 according to the present embodimentshown in FIG. 1, an ENUM system was realized due to the numbermanagement apparatuses 10 including a function (the function of numberresolution unit 12) of responding to the query (request) for connectiondestination information from the SIP server or the like.

In contrast to this, when the ENUM system is to be realized, the numbermanagement system 1 a according to Variation 1 of the present embodimentis characterized by executing a function of responding to a query(request) for connection destination information from the SIP server orthe like (function of the number resolution unit 12) using an apparatus(ENUM server) separate from the number management apparatus 10.

FIG. 8 is a diagram showing an overall configuration of an ENUM systemincluding a number management system 1 a according to Variation 1 of thepresent embodiment.

As shown in FIG. 8, the number management apparatuses 10 (10A, 10B, 10C)included in the number management system 1 a are connected to ENUMservers 20 (20A, 20B, 20C) installed by respective communicationproviders. The ENUM server 20 includes a data update unit 14 in additionto the configuration of the number resolution unit 12 and the numberdatabase 13 shown in FIGS. 1 and 3. Also, the number managementapparatus 10 includes a number portability information transmission unit115 in addition to the configuration of the number management unit 11shown in FIG. 1. That is, in the present embodiment, although the numbermanagement unit 11 and the number resolution unit 12 are provided inseparate apparatuses, it can be said that they are in a correspondencerelationship due to being under the management of the same provider.

Note that configurations having the same function as the numbermanagement apparatuses 10 shown in FIGS. 1 and 3 are denoted by the samereference numerals and names, and description thereof is omitted.

If a new block is stored connected to a blockchain due to the blockapproval unit 114 approving the suggested block, the number portabilityinformation transmission unit 115 extracts the number portabilityinformation, which is information of the transactions included in thenewly-stored block. The number portability information transmission unit115 transmits the number information update request including the numberportability information to the ENUM server 20 of the communicationprovider to which the number portability information transmission unit115 belongs. Also, from the ENUM server 20, the number portabilityinformation transmission unit 115 receives a number information updateresponse, which is a response to the number information update requestand indicates that the number database has been updated using thetransmitted number portability information.

<Enum Server>

The ENUM server 20 is an apparatus (number resolution apparatus) thatreceives a query (request) for connection destination information for atelephone number of a terminal serving as a connection destination fromthe SIP server or the like and sends a response. This ENUM server 20includes a number resolution unit 12, a data update unit 14, and anumber database (DB) 13.

The number resolution unit 12 receives a query from the SIP server orthe like, references the number database 13 to extract the connectiondestination information corresponding to the telephone number indicatedby the query, and transmits the result to the SIP server or the like.

The data update unit 14 receives a number information update requestfrom the number management apparatus 10 connected to the data updateunit 14, and updates the number database 13 using the number portabilityinformation included in the number information update request. Then,when the update of the number database 13 is complete, the data updateunit 14 transmits the number information update response indicating thatthe update is complete to the number management apparatus 10.

FIG. 9 is a sequence diagram showing a flow of processing performed byan ENUM system including a number management system 1 a according toVariation 1 of the present embodiment.

Since the processing (steps S1 to S9) of the number management system 1indicated by FIG. 6 is the same, the description thereof is omitted.

When the block approval units 114 (FIG. 3) of the number managementapparatuses 10 (10A, 10B, 10C) approve the suggested block (step S9),the number portability information transmission units 115 (not shown inFIG. 9) extracts the number portability information, which isinformation on the transactions included in the blocks that were newlystored in the blockchain. Then, the number portability informationtransmission unit 115 generates a number information update requestincluding the extracted pieces of number portability information andtransmits it to the ENUM server 20 of the communication provider towhich the number portability information transmission unit 115 belongs(step S10).

Next, upon receiving the number information update request, the dataupdate units 14 of the ENUM servers 20 updates the number database 13using the number portability information included in the numberinformation update request (step S11).

Next, when the update of the number database 13 is completed, the dataupdate unit 14 of each ENUM server 20 transmits a number informationupdate response indicating that the update is complete to the numbermanagement apparatus 10 (step S12).

Note that the processing performed during number resolution is the sameas in the sequence shown in FIG. 7, and therefore description thereof isomitted.

By doing so, the number management apparatuses 10 of the numbermanagement system 1 a can reflect the updated number portabilityinformation in the number database 13 of the ENUM server 20 of thecommunication provider to which the number management apparatus 10belongs.

Note that instead of receiving the number update request from the numbermanagement apparatus 10, the data update unit 14 of the ENUM server 20may also receive the number portability information from the numberportability information transmission unit 115 of the number managementapparatus 10 and update the number database 13 by transmitting theacquisition request for the updated number portability information at apredetermined time interval from the data update unit 14.

<<Variation 2>>

Although the block suggestion unit 113 was provided in all of the numbermanagement apparatuses 10 creating the blockchain in the numbermanagement system 1 shown in FIG. 1, in Variation 2, one of the numbermanagement apparatuses 10 creating the blockchain is set as therepresentative (leader) number management apparatus 10. Also, aconfiguration is used in which the block suggestion unit 113 is includedin the representative number management apparatus 10 (e.g., 10A) and theblock suggestion unit 113 is not included in the other number managementapparatuses 10 (10B, 10C).

With the transaction generation unit 112 (FIG. 3) of each numbermanagement apparatus 10 according to the present embodiment, the numberupdate suggestion is received from the request reception unit 111, and atransaction is generated for the number portability information.Thereafter, the request reception unit 111 (or the transactiongeneration unit 112) transmitted the number update instruction to theblock suggestion unit 113 of any number management apparatus 10 creatingthe blockchain, which was determined based on the predetermined logic(block suggestion unit selection logic).

In contrast to this, with the number management apparatus 10 accordingto Variation 2 of the present embodiment, the request reception unit 111(or transaction generation unit 112) of the number managementapparatuses 10 (10B, 10C) is characterized by transmitting the numberupdate instruction to the block suggestion unit 113 of therepresentative number management apparatus 10 (10A). Then, the blocksuggestion unit 113 of the representative number management apparatus 10(10A) aggregates the received number update instruction and generates ablock including multiple transactions. Next, the block suggestion unit113 transmits the number update approval request including the generatedblock to the block approval unit 114 of the number managementapparatuses 10 creating in the blockchain.

When the normality of the block included in the number update request isto be confirmed, the block approval unit 114 of the number managementapparatus 10 may also confirm the normality, as well as the fact thatthe transmission source is the representative number managementapparatus 10 (10A).

By doing so as well, the number management apparatuses (blockchaincreation apparatuses) 10 of the number management system 1 according toVariation 2 of the present embodiment can store the number portabilityinformation of all members (communication providers) that participate inthe blockchain, instead of the number portability information relatingto the telephone number managed by the number management apparatus 10.Accordingly, it is possible to improve the availability of the numberportability information that is used in the ENUM system. Also, forexample, since the problems (sequentiality, consistency, atomicity) withthe agreement form of the dispersed system that occurs in a case inwhich multiple block suggestion units 113 are present in a blockchainneed not be dealt with, it is possible to reduce the processing load andcommunication load in the overall system.

<<Variation 3>>

Next, Variation 3 of the number management system 1 according to thepresent embodiment will be described.

The number management system 1 according to the present embodiment (seeFIG. 1) is premised not on a publicly-open type of blockchain thatanyone can participate in, but on a Permissioned type of blockchain thatuses a service in which a blockchain is used among limited members. Inthis case, communication providers to which telephone numbers have beendispensed by the Ministry of Internal Affairs are envisioned as memberswho can transmit the number update request to the number managementapparatus 10. However, a case is also conceivable in which the Ministryof Internal Affairs dispenses numbers directly to users in the future.In this case, users to whom the Ministry of Internal Affairs hasdispensed numbers may also be included in the “Permissioned” targets.

Accordingly, the number management system according to Variation 3 usesa configuration in which not only communication providers but alsospecific users (user terminals) can transmit number update requests tothe number management apparatus 10. Also, if the number managementapparatus 10 includes the function of an ENUM server, the numbermanagement apparatus 10 may also receive a query about the connectiondestination information corresponding to the telephone number directlyfrom the user terminal without going through an SIP server of acommunication provider, and may resolve the number.

Effects

As described above, the number management system of the presentinvention is a number management system 1 including a plurality ofnumber management apparatuses 10 for managing number portabilityinformation including a telephone number and connection destinationinformation for the telephone number, in which the plurality of numbermanagement apparatuses 10 each include a number management unit 11configured to manage the number portability information as a blockchain,and a number resolution unit 12 configured to send the connectiondestination information corresponding to a query telephone number as aresponse, the number management unit 11 includes a request receptionunit 111 configured to receive a number update request including thenumber portability information, a transaction generation unit 112configured to generate a transaction including encrypted connectiondestination information obtained by encrypting the connectiondestination information included in the number portability informationusing a predetermined encryption key, and the telephone number, a blocksuggestion unit 113 configured to acquire the transactions generatedaccording to a plurality of said number update requests, generate anewly-suggested block including a transaction group obtained byaggregating the acquired plurality of transactions, and transmit thegenerated suggested block to the respective plurality of numbermanagement apparatuses creating the blockchain, and a block approvalunit 114 configured to receive the suggested block, approve thesuggested block by confirming a predetermined normality of the suggestedblock, and store the suggested block by connecting the suggested blockto a block stored as the blockchain in a storage unit, and the numberresolution unit 12 includes a query reception unit 121 configured toreceive a query request including the query telephone number, a datamanagement unit 122 configured to search transactions in the blockchainusing the query telephone number as a key and extract the encryptedconnection destination information corresponding to the query telephonenumber, and a decryption processing unit 123 configured to decrypt theencrypted connection destination information using a decryption key andsend the connection destination information corresponding to the querytelephone number as a response.

By doing so, the number management apparatuses 10 (blockchain creationapparatuses) of the number management system 1 can store not only thenumber portability information relating to the telephone numbers managedby the number management apparatuses 10, but also the number portabilityinformation of all members (communication providers, etc.) participatingin the blockchain. Accordingly, it is possible to improve theavailability of the number portability information that is used in theENUM system.

Also, according to the number management system 1, due to a portion(connection destination information) of the number portabilityinformation being encrypted and stored in a blockchain, it is possibleto improve the confidentiality of the number portability information,and it is possible to reduce the risk of information leakage that isincreased by sharing the number portability information with all members(communication service providers, etc.).

Also, in the number management system 1, the decryption keycorresponding to the encryption key to be used by the decryptionprocessing unit 123 is held by one of the plurality of number managementapparatuses 10, the transaction generation unit 112 generates thetransaction as well as identification information for identifying thenumber management apparatus 10 holding the decryption key, and the datamanagement unit 122 extracts the encrypted connection destinationinformation and the identification information, and the query receptionunit 121 requests decryption of the encrypted connection destinationinformation to the decryption processing unit 123 of the numbermanagement apparatus 10 identified by the extracted identificationinformation, and acquires the connection destination informationcorresponding to the query telephone number.

In this manner, due to allowing one of the multiple number managementapparatuses 10 to hold the decryption key corresponding to theencryption key, a query to another provider is generated, and thereforethat action will be discovered, which serves as a deterrent, making itpossible to more reliably prevent unauthorized use of number portabilityby a provider.

Also, in the number management system 1, the decryption keycorresponding to the encryption key is held by a plurality of the numbermanagement apparatuses 10.

By doing so, it is possible to continue number resolution processing inthe overall system even if breakdown occurs in a specific numbermanagement apparatus 10, and thus it is possible to improve theavailability of the number portability information.

Note that the number management system 1, the number management method,and the number management apparatus 10 according to the presentinvention is not limited to the above-described embodiments andvariations, and changes can be implemented in a range that does notdepart from the gist of the present invention.

For example, in the present embodiment, the number portabilityinformation was described as a set of a telephone number and changedconnection destination information (accepting provider information). Inaddition to this, for example, the number portability information mayalso be formed as a set composed of a telephone number, unchangedaccepting provider information, and changed accepting providerinformation. In this case as well, effects similar to those of thepresent embodiment can be exhibited.

REFERENCE SIGNS LIST

-   1, 1 a Number management system-   10 (10A, 10B, 10C) Number management apparatus-   11 Number management unit-   12 Number resolution unit-   13 Number database-   14 Data update unit-   20 ENUM server-   111 Request reception unit-   112 Transaction generation unit-   113 Block suggestion unit-   114 Block approval unit-   115 Number portability information transmission unit-   121 Query reception unit-   122 Data management unit-   123 Decryption processing unit

1. A number management system including a plurality of number managementapparatuses for managing number portability information including atelephone number and connection destination information for thetelephone number, wherein the plurality of number management apparatuseseach include a number management unit, including one or more processors,configured to manage the number portability information as a blockchain,and a number resolution unit, including one or more processors,configured to send the connection destination information correspondingto a query telephone number as a response, the number management unitincludes a request reception unit, including one or more processors,configured to receive a number update request including the numberportability information, a transaction generation unit, including one ormore processors, configured to generate a transaction includingencrypted connection destination information obtained by encrypting theconnection destination information included in the number portabilityinformation using a predetermined encryption key, and the telephonenumber, a block suggestion unit, including one or more processors,configured to acquire the transactions generated according to aplurality of said number update requests, generate a newly-suggestedblock including a transaction group obtained by aggregating an acquiredplurality of transactions, and transmit the generated suggested block tothe respective plurality of number management apparatuses creating theblockchain, and a block approval unit, including one or more processors,configured to receive the suggested block, approve the suggested blockby confirming a predetermined normality of the suggested block, andstore the suggested block by connecting the suggested block to a blockstored as the blockchain in a storage unit, and the number resolutionunit includes a query reception unit, including one or more processors,configured to receive a query request including the query telephonenumber, a data management unit, including one or more processors,configured to search transactions in the blockchain using the querytelephone number as a key and extract the encrypted connectiondestination information corresponding to the query telephone number, anda decryption processing unit, including one or more processors,configured to decrypt the encrypted connection destination informationusing a decryption key and send the connection destination informationcorresponding to the query telephone number as a response.
 2. The numbermanagement system according to claim 1, wherein the decryption keycorresponding to the encryption key to be used by the decryptionprocessing unit is held by one of the plurality of number managementapparatuses, the transaction generation unit is configured to generatethe transaction as well as identification information for identifyingthe number management apparatus holding the decryption key, and the datamanagement unit is configured to extract the encrypted connectiondestination information and the identification information, and thequery reception unit is configured to request decryption of theencrypted connection destination information to the decryptionprocessing unit of the number management apparatus identified by theextracted identification information, and acquire the connectiondestination information corresponding to the query telephone number. 3.The number management system according to claim 2, wherein thedecryption key corresponding to the encryption key is held by aplurality of the number management apparatuses.
 4. A number managementmethod for a number management system including a plurality of numbermanagement apparatuses for managing number portability informationincluding a telephone number and connection destination information forthe telephone number, the method comprising: receiving, by a numbermanagement apparatus, a number update request including the numberportability information; generating, by the number management apparatus,a transaction including encrypted connection destination informationobtained by encrypting the connection destination information includedin the number portability information using a predetermined encryptionkey, and the telephone number; acquiring, by the number managementapparatus, acquiring the transactions generated according to a pluralityof said number update requests, generating a newly-suggested blockincluding a transaction group obtained by aggregating the acquiredplurality of transactions, and transmitting the generated suggestedblock to the respective plurality of number management apparatusescreating a blockchain; receiving, by the number management apparatus,receiving the suggested block, approving the suggested block byconfirming a predetermined normality of the suggested block, and storingthe suggested block by connecting the suggested block to a block storedas the blockchain in a storage unit; receiving, by the number managementapparatus, a query request requesting the connection destinationinformation corresponding to a query telephone number; searching, by thenumber management apparatus, transactions in the blockchain using thequery telephone number as a key and extracting the encrypted connectiondestination information corresponding to the query telephone number; anddecrypting, by the number management apparatus, the encrypted connectiondestination information using a decryption key and sending theconnection destination information corresponding to the query telephonenumber as a response.
 5. A number management apparatus in a numbermanagement system including a plurality of the number managementapparatuses for managing number portability information including atelephone number and connection destination information for thetelephone number, wherein the number management apparatus includes anumber management unit including one or more processors, configured tomanage the number portability information as a blockchain and a numberresolution unit, including one or more processors, configured to sendthe connection destination information corresponding to a querytelephone number as a response, the number management unit includes arequest reception unit, including one or more processors, configured toreceive a number update request including the number portabilityinformation, a transaction generation unit, including one or moreprocessors, configured to generate a transaction including encryptedconnection destination information obtained by encrypting the connectiondestination information included in the number portability informationusing a predetermined encryption key, and the telephone number, a blocksuggestion unit, including one or more processors, configured to acquirethe transactions generated according to a plurality of said numberupdate requests, generate a newly-suggested block including atransaction group obtained by aggregating the acquired plurality oftransactions, and transmit the generated suggested block to therespective plurality of number management apparatuses creating theblockchain, and a block approval unit, including one or more processors,configured to receive the suggested block, approve the suggested blockby confirming a predetermined normality of the suggested block, andstore the suggested block by connecting the suggested block to a blockstored as the blockchain in a storage unit, and the number resolutionunit includes a query reception unit, including one or more processors,configured to receive a query request including the query telephonenumber, a data management unit, including one or more processors,configured to search transactions in the blockchain using the querytelephone number as a key and extract the encrypted connectiondestination information corresponding to the query telephone number, anda decryption processing unit, including one or more processors,configured to decrypt the encrypted connection destination informationusing a decryption key and send the connection destination informationcorresponding to the query telephone number as a response.
 6. (canceled)7. The number management method according to claim 4, wherein thedecryption key corresponding to the encryption key to be used by adecryption processing unit is held by one of the plurality of numbermanagement apparatuses, and generating the transaction as well asidentification information for identifying the number managementapparatus holding the decryption key, and extracting the encryptedconnection destination information and the identification information,and requesting decryption of the encrypted connection destinationinformation to the decryption processing unit of the number managementapparatus identified by the extracted identification information, andacquiring the connection destination information corresponding to thequery telephone number.
 8. The number management method according toclaim 7, wherein the decryption key corresponding to the encryption keyis held by a plurality of the number management apparatuses. wherein thedecryption key corresponding to the encryption key to be used by thedecryption processing unit is held by one of the plurality of numbermanagement apparatuses, the transaction generation unit is configured togenerate the transaction as well as identification information foridentifying the number management apparatus holding the decryption key,and the data management unit is configured to extract the encryptedconnection destination information and the identification information,and the query reception unit is configured to request decryption of theencrypted connection destination information to the decryptionprocessing unit of the number management apparatus identified by theextracted identification information, and acquire the connectiondestination information corresponding to the query telephone number.wherein the decryption key corresponding to the encryption key is heldby a plurality of the number management apparatuses.